HUMAN NUTRITION DIGESTION DISSECTION 28 MAY 2014

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1 HUMAN NUTRITION DIGESTION DISSECTION 28 MAY 2014 In this lessn, we: Lessn Descriptin Study the structure f the digestive system f animal by ding a dissectin Summary Structure f the Digestive System The digestive system is cmpsed f the fllwing parts: Muth with teeth and salivary glands t begin the prcess f digestin. Oesphagus that cnnects the muth t the stmach. Stmach is where the fd underges bth mechanical and chemical digestin. Small intestine is where the digested fd underges the final step f digestin and where the majrity f substances are absrbed frm the digested fd. Large intestine is where water is absrbed frm the fd and faeces are frmed. Prcesses used in the digestive used Nutritin is defined as the sum f the fllwing prcesses ingestin, digestin, absrptin, assimilatin and egestin. Sme definitins that yu need t knw: Ingestin is the prcess where fd is taken in this ccurs in the muth. Digestin is the prcess where large mlecules are brken dwn int smaller mlecules either mechanically r chemically. Absrptin is the prcess where the mlecules mve thrugh the intestinal walls (small intestine) int the bld vessels. Assimilatin is the prcess where nutrients are mved int and used by the cell. Egestin is the prcess whereby unused nutrients are eliminated frm the digestive system. Organs and glands assciated with the digestive system The salivary glands situated in the muth prduce an enzyme called amylase that begins the digestin f starches and carbhydrates. The Liver prduces bile and breaks dwn amin acids, alchl, hrmnes and drugs. The Gall Bladder stres bile prduced by the liver The pancreas prduces insulin, glucagn and pancreatic juice. The stmach cntains cells that prduce and secrete hydrchlric acid.

2 Types f Digestin Mechanical digestin starts in the muth with the teeth chewing the fd and the tngue wrking the fd int a ball (blus) fr swallwing. The Bilgical name fr chewing is masticatin. The blus is mved t the back f the muth and pushed int the esphagus where mre mechanical digestin ccurs in the frm f peristalsis. Peristalsis in the prcess where muscles in the wall f the esphagus cntract and relax antagnistically. This means when ne muscle cntracts. The ther muscle relaxes and s it cntinues alternating cntracting and relaxing. Peristalsis als happens in the stmach and the rest f the digestive tract t push the fd alng. Anther frm f mechanical digestin ccurs in the stmach where the stmach muscles churn the fd int a liquid called chyme. (Slutins fr all Life Sciences, Macmillan, p155) Chemical digestin uses enzymes t break the fd int its basic chemical cmpunds fr absrptin by the bdy. The enzymes cntrl the chemical breakdwn. The enzymes are sensitive t temperature and ph. Different enzymes act in different ph levels in the varius parts f the digestive system. There are a large number f glands and rgans assciated with the digestive system. They prvide chemical substances that enhance the chemical digestin f fd.

3 Digestive secretin Where prduced Enzymes Functins f enzyme/s ph Saliva Salivary glands Carbhydrases Cked starches - maltse Alkaline (6 7) Gastric juice Glands in stmach Prteases Prteins plypeptides Acid(3) Pancreatic juice Pancreas Carbhydrases Prteases Starches maltse Prteins plypeptides Alkaline (8) Intestinal juice Glands in small intestine Carbhydrases Prteases Maltse glucse Plypeptides amin acids Alkaline (8) Fats fatty acids & glycerl Lipases Absrptin (Taken frm Series Life Sciences p 125) Absrptin is defined as the prcess where the prducts f digestin (small mlecules) mve thrugh the wall f the small intestine int the bld vessels. Absrptin can ccur in the muth, stmach and large intestine but the majrity f the absrptin ccurs in the small intestine. Water is absrbed mainly in the large intestine. Fr absrptin t ccur prperly, there are a few criteria that the small intestine must meet: There must be a large surface area s that a lt f nutrients can be absrbed. The surface f the intestine must be thin s that the smaller mlecules can be absrbed. There must be a gd bld supply s that the absrbed mlecules can be mved thrughut the bdy The mlecules inside the intestine must be in clse cntact with the surface the mlecules must be small Structure f a Villus A villus is a finger-like prjectin which increases the surface area. There are many tiny bld vessels (capillaries) t carry away amin acids, mnsaccharadies, mineral salts and vitamins which pass thrugh the villus. Water is reabsrbed because the amin acids, minerals etc are in slutin t be absrbed. In the centre f the villus is a lacteal which carries lipids t the lymph vessels. The epithelium f each villus has flds in the membrane frming micrvilli knwn as a brush brder. There is nly ne layer f clumnar epithelium s that it is easy fr the small mlecules t mve frm the lumen f the small intestine int the villus. The Gblet cells fund interspersed amngst the clumnar epithelium secrete mucus. Between each villus is fund a krypt f Lieberkuhn. The krypts prduce new cells t replace any cells that need t be replaced. The Brunner s glands prduce an alkaline slutin which cntains bicarbnate.

4 Assimilatin The prcess where nutrients are taken frm the bld and int the cells is called assimilatin. Absrbed nutrients are transprted frm the liver t the heart by the hepatic vein. Frm the heart the nutrients mve t all parts f the bdy. Nutrient / Chemical Amin acids Glucse Alchl and drugs Hrmnes Hepatic Prtal System Prcess Excess amin acids g thrugh a prcess f de-aminatin. De-aminatin is when the nitrgen is remved and ammnia is frmed with it The ammnia is mved t the kidneys which cnvert it int urea. The urea is excreted in the urine. Excess glucse is cnverted int glycgen. The liver stres the glycgen which can be cnverted back int glucse when needed. The detxificatin prcess changes alchl and drugs frm harmful substances int harmless substances Excess alchl ver time causes the liver t wrk t hard and this leads t sme parts f the liver nt wrking. Once hrmnes have fulfilled their functins in the bdy, the liver breaks them dwn. Examples are insulin, teststerne and estrgen. The capillaries jin t frm venules. The venules jin with venules frm the stmach t becme the hepatic prtal vein. This system is knwn as the hepatic prtal system. The hepatic prtal vein transprts amin acids and glucse mlecules t the liver. The hepatic prtal vein is unusual because it is frmed by a series f capillaries that jin tgether utside the liver and then split up int capillaries again inside the liver.

5 (Slutins fr all Life Sciences, Macmillan, p161) Egestin Sme substances in the fd that the digestive system cannt digest. This undigested waste is remved frm the bdy thrugh the prcess f egestin. Egestin is the remval f undigested fd thrugh the anus in the frm f faeces.

6 Questin 1 Test Yurself Which is nt true f peristalsis? A. it enables defaecatin B. it causes the frward mvement f fd alng the gut C. enables yu t swallw even when standing n yur head D. is a vluntary actin Questin 2 Lipase a fat digesting enzyme is fund in: A. saliva B. gastric juice C. pancreatic juice D. intestinal juice Questin 3 What prcess causes the digestin f the macr-nutrients starch, prteins and fats? A. hydrlysis B. glyclysis C. phtlysis D. cndensatin synthesis Questin 4 A prtein mlecule will be digested by enzymes secreted by: A. the muth, stmach and cln B. the stmach, liver and small intestine C. the small intestine. muth and liver D. the small intestine, pancreas and stmach Questin 5 Digestin in the lumen f the stmach is limited t A. carbhydrates B. fats C. prteins D. Nne f the abve. All kinds f fd is digested here

7 Questin 6 Which f the fllwing des nt ccur in the muth? A. lubricatin f the fd B. beginning f prtein digestin C. breaking the fd int small fragments D. all f the abve Questin 7 If the pancreas is remved, the cmpund which remains undigested is A. prteins B. carbhydrates C. fats D. prteins and carbhydrates Questin 8 Digestin takes place in each f the fllwing rgans except: A. large intestine B. stmach C. small intestine D. muth